1. Technical Field
The present invention generally relates to redundant arrays of inexpensive disks (RAID). More particularly, it relates to an air circulation system that operates according to the environmental conditions of the RAID's interior, and it further relates to a method of controlling the air circulation cycle within the RAID.
2. Related Art
The efficiency of computer systems is dependent on the performance of a central processing unit (CPU) and its input/output (I/O) subsystem. With the development of VLSI technology, the data processing time of the CPU has been significantly reduced, while operating speeds of the I/O subsystem have improved relatively less. Thus, the proportion of data I/O time to the overall system operating time is increasing. Also, when a malfunction occurs in the I/O subsystem, the costs of recovering data stored in the failed system has increased. In recent years, the demand for high performance high-reliability I/O subsystems has increased and, to meet this demand, some remarkable research and development have been devoted to RAID systems. RAID related techniques have become common.
Academic institutions are conducting research on RAID algorithms, and enterprises are striving for RAID systems with higher capacities and improved reliability through various performance tests. Disk arrays have been used for super computers, such as those built by the Cray Computer Company, to improve I/O throughput from hard disks. Computer scientists at Berkeley University, USA created the first RAID theory in 1988. Although RAID theory can be applied to sequential access devices, such as cartridge tapes, most attention is being focused on hard disk devices.
Traditional disk devices are typically single large expensive disks (SLED) having form factors of 12 or 14 inches. The wide use of personal computers has created a market for inexpensive small form factor drives. Consequently, a disk storage device having a redundant array of inexpensive disks has become a practical alternative for storing large amounts of data. The primary objective of RAID systems is to create higher storage capacities and faster I/O throughput using stripping. Stripping involves the concurrent transfer of data to an array of disk drives in "stripes". RAID architectures are divided into the following six levels by application environments and the characteristics of computer systems to which RAID is applied:
RAID level 0:
RAID level 0 distributes the data over all of the drives in the array. It focuses on the disk performance rather than on the disk reliability.
RAID level 1:
Mirroring is one of the traditional techniques used with RAID systems to improve disk performance. With this technique, all data on the disks should be and are simultaneously stored on copy disks, which is not cost-effective. RAID level 1 is limited since the actually usable disk capacity is 50%, and is not advantageous to a system needing large-capacity disks, such as a database system. However, since the same data are stored on the copy disks, RAID level 1 is the best way to keep the data secure.
RAID level 2:
RAID level 2 was developed in order to reduce the costs of keeping data secure, and distributes data over all of the drives in the array by bytes. RAID level 2 has several test disks for error detection and error correction in addition to the data storage disks.
RAID level 3:
RAID level 3 reads and writes data from and into N data plus P parity direct access storage devices synchronously. Parity data are stored in extra parity drives, and disk spindles are synchronized so that data are input to and output from all of the drives in an array simultaneously, which increases the data rate even if data input and output do not occur synchronously. If a drive in the array fails, it is possible to reconstitute the data from the failed drive using the remaining drives and parity drives, although the overall data rate is decreased. RAID level 3 is used in application systems, super computers, image manipulation processors, etc.
RAID level 3 is the most efficient in the transmission of large blocks of data, but is disadvantageous in the transmission of small blocks of data and responding to rapid I/O requests. Additionally, with RAID level 3, a single large expensive drive is required for redundancy along with data storage drives. While RAID level 3 has fewer drives than RAID level 1 does, it needs a complicated, and thus expensive, controller.
RAID level 4:
RAID level 4 stores parity data on the same drive with data stripped across an array of disks, where one block of a stripe is reserved for parity data. It is possible for RAID level 4 to restore data stored on a failed drive. The data-read performance is similar to that of RAID level 1, but the data-write performance is inferior because RAID level 4 stores parity data on the same drive. To alleviate the drawbacks of RAID level 4, RAID level 5 has been developed.
RAID level 5:
In RAID level 5, data are stripped across an array of drives. RAID level 5 distributes the parity blocks over all of the drives in the array for the purpose of precluding a bottleneck during write operations. It is required to read the data written into all the drives in the array so as to recalculate parity during data write operations, which increases its data processing time. In RAID level 5, data input/output processing is possible, and missing data from a failed drive can be recreated. Accordingly, RAID level 5 is suitable for large blocks of data and, if an application program for RAID level 5 focuses on data reading, or if writing performance can be improved, RAID level 5 also may have advantages with small blocks of data.
With the decreased size of data blocks, RAID level 5 may assure a degree of efficiency and data availability. RAID level 5 offers a cost-effective solution, compared to a non-array device.
The above-described disk arrays are equipped with cooling systems, but their hard disk drives are particularly sensitive to ambient temperature and humidity, and may encounter off-tracking of their servo-systems due to disk deformation resulting in read/write errors. In addition, the disk surface may be stained with dirt and dust or corroded by gas, thereby causing fatal disk failures. Each of the RAID systems uses a cooling system, whereby fresh air continuously enters and is circulated inside the RAID system, thus driving out bad air. This cooling system may prevent the RAID systems' interior from being contaminated or overheating. As described above, the cooling system for a RAID system is used to prevent the system from failing due to environmental factors, (ambient temperature, humidity, etc.), such as heat emitted from its hard disk drive and power supply, surface temperatures of the system body, polluted interior air of the system, etc.
The following patents are considered to be representative of the art relative to the invention disclosed and claimed herein: U.S. Pat. No. 5,438,226 to Kuchta, entitled Apparatus For Redundant Cooling Of Electronic Devices, U.S. Pat. No. 5,471,099 to Larebell et al., entitled Modular Enclosure Apparatus, U.S. Pat. No. 5,586,250 to Carbonneau et al., entitled SCSI-Coupled Coupled Module For Monitoring And Controlling SCSI Coupled RAID Bank And Bank Environment, U.S. Pat. No. 4,500,944 to Roberts et al., entitled Enclosure For Electronic Components, U.S. Pat. No. 4,512,161 to Logan et al., entitled Dew Point Sensitive Computer Cooling System, U.S. Pat. No. 4,685,303 to Branc et al., entitled Disc Drive Isolation System, U.S. Pat. No. 4,774,631 to Okuyama et al., entitled Cooling Structure Of Electronic Equipment Rack, U.S. Pat. No. 5,102,040 to Harvey, entitled Method And Apparatus For Fan Control To Achieve Enhanced Cooling, U.S. Pat. No. 5,570,838 to Davis Jr. et al., entitled Method And Control System For Controlling An Automotive HVAC System For Increased Occupant Comfort, U.S. Pat. No. 5,572,403 to Mills, entitled Plenum Bypass Serial Fan Cooling Subsystem For Computer Systems, U.S. Pat. No. 5,655,375 to Ju, entitled Antenna Mast-Top Mountable Thermo-Electrically Cooled Amplifier Enclosure System, U.S. Pat. No. 3,682,381 to Eckman et al., entitled Air Conditioning Apparatus, U.S. Pat. No. 3,599,063 to Nanai, entitled Speed Control System For D.C. Motor, U.S. Pat. No. 3,585,811 to Friedel, entitled Air Conditioned Storage System, U.S. Pat. No. 3,976,925 to Rudich Jr., entitled Integral Motor Controller, U.S. Pat. No. 3,991,624 to Davies, entitled Wind Velocity Servo System, U.S. Pat. No. 4,818,924 to Burney, entitled Electric Actuator For Automotive Air Conditioning Systems, U.S. Pat. No. 4,848,444 to Heinle et al, entitled Process And Processor For The Control Of Parameters Of The Interior Air In A Motor Vehicle Having An Air Conditioning System, U.S. Pat. No. 4,910,445 to Borrmann, entitled Actuating Device For Movable Parts For Closing Of Apertures In Vehicles And Vehicle Roof Utilizing Same, U.S. Pat. No. 5,021,726 to Reinhardt et al., entitled Process For Driving An Alternating-Current Motor And An Alternating Current Motor Which Can Be Driven In Accordance With This Process, and U.S. Pat. No. 3,765,244 to Brzezinski, entitled Digital Readout Instrument Employing Transducer And Double D.C. Power Supply.
Of the patent listed above, only the following relate to RAID systems: Kuchta '226; Larabell et al. '099; Carbonneau et al. '250. Each of these patents relates, at least generally, to the control of the environment in the RAID system (for example, control of temperature). However, none of the patents discloses an arrangement or method for controlling both temperature and humidity in the RAID system, and none of the patents discloses an arrangement or method which controls temperature and humidity conditions with the precision necessary in order to ensure proper and sustained operation of the RAID system.
The following patents disclose arrangements or methods for controlling the environment surrounding electronic components in general: Roberts et al. '944; Logan et al. '161; Branc et al. '303; Okuyama et al. '631; Harvey '040; Davis Jr. et al. '838; Mills '403; and Ju et al. '375. However, none of these patents relates to the control of an environment surrounding an RAID system, with its unique requirements for precision-controlled environmental conditions, and none of the latter patents discloses or suggests the method and arrangement disclosed and claimed herein.
Finally, the remaining patents listed above do not relate to the control of environmental conditions within an enclosure housing electronic components, and do not disclose or suggest the method and arrangement disclosed and claimed herein.